Japanese Laid-Open Patent Publication No. 2005-238787 (hereinafter “Document 1”) discloses an ink discharge amount measuring method for measuring the discharge amount of an ink droplet discharged from a nozzle of an ink jet head. This method finds the ink discharge amount by carrying out a step of discharging an ink droplet from a nozzle onto an ink droplet shape evaluating jig, a step of measuring the diameter of the ink droplet discharged onto the ink droplet shape evaluating jig, and a step of calculating the ink discharge amount from the diameter of the measured ink droplet based on correlation found in advance between the diameter of an ink droplet and the ink discharge amount.